RMS?
Seems to me the way to go, Jan...Do I convert the dB numbers back to voltage ratio, RMS sum the voltage ratios and then convert to dB?
Jan
Hi Jan,
It would seem to me that you can't add these numbers directly. The resulting number we get from the meter is like a DC value on a meter, but it is derived from a chaotic waveform composed of noise from every connection that exists while you are measuring. I think you would have to add the squares and take the root in order to get a good guesstimate.
Nothing in electronics is that easy as a scalar addition of two entirely different wave forms unless the delta T approaches 0.
-Chris
Hi Jan,
That's the point. Measurement uncertainty.
If you used a spec-an, you could read what is a harmonic and what isn't. That might help the confidence aspect.
-Chris
Couldn't you just convert into percentages and add those for a total?
Doing just that with your given numbers (-110dB + -105dB) gives me a total of 0.0008785% or -101.1251dB.
No idea if that is anywhere near reality though. Someone else would have to disprove or confirm.
Not sure if the limited number of decimal points of the online calculator I used is sufficiently accurate though.
If I treat the numbers as dBV, convert to Vrms, compute the difference and then back to dB I get -106.5dB with a generator that has -110dBV and a result of -105dBV. Not sure that's correct though.
Jan
Unless you know the phase of each component you have to do an RMS calculation as a best guess. Only if you know that the sig gen and circuit generate a given harmonic at the same phase can you do a straight arithmetic difference.
Hmmm. Interesting approach, although it would be a bit different for my numbers because -105 is the result of a generator at -110 and ´X´ resulting in finally -105. So in your approach X would be -110 - -105. I think.
Jan